Spas primarily but also pools have water recirculation systems which operate at high speeds to massage the body and to continually reheat the circulating water. Accidents can occur when the water temperature reaches too high a level, for example hyperthermia and death may result from too long an exposure to too high a temperature of water. Heaters typically are equipped with flow sensing and high temperature limit switches which shut down the heater when there is no water flow and when the heater, usually sensed at the housing, has reached a preset maximum temperature indicative of the onset of too hot water coming from the heater.
Pumps used to recirculate the water are also sources of heat particularly at the high circulation speeds preferred by spa users. But at present there is no way to monitor the undue input of heat into the water from the pump or to stop its buildup automatically. Thus dangerous water temperatures may occur although the heater has shut down.